Latest installed is almost exactly not what you want, I've had plenty
(where plenty in this case is probably >5) of cases where a kernel
update broke something, in quite a few of those cases to a state where
the system wouldn't boot. If the most recent one is retained then
you've still got a kernel, but not one that will actually run. With
current behaviour I can still let my system update until a fix appears
because I know it won't remove the good kernel. If updates can remove
the running kernel then you have to watch each one carefully.
Right, so if you run into a situation where you need to run an old
kernel-0.99, you'd protect it